1. Field of the Invention
This invention relates generally to a rotor device, and more particularly to a rotor device for use as a compressor in a supercharger that is driven at high rotational speeds.
2. Description of the Prior Art
Generally, a prior art rotor device that increases the quantity of air discharged as a result of a decrease in the dead space in the rotor is disclosed in Japanese Patent Laid-open No. 61(1986)-4802 published on Jan. 10, 1986. As shown in FIG. 4, the rotor device of the prior art includes outer and inner rotors 120 and 130 that are disposed within a casing 100 and that rotate around their respective rotational axes. In response to rotation of the outer and inner rotors 120, 130, the outer sealing portion of the inner rotor 130 defines a locus along an inner wall surface of the operating chamber of the outer rotor 120.
An inner sealing portion of the outer rotor 120 defines a locus along an outer circumferential surface of the inner rotor 130 as a result of rotations of the outer and inner rotors 120 and 130. The outer circumferential surface of the inner rotor 130 engages the inner wall surface forming an operating chamber of the outer rotor 120 through a gear engagement. Since the input pulley 131 is connected to the inner rotor 130, the outer bearing 121 for the outer rotor 120 must be arranged at the outer circumferential portion of the rotating shaft of the inner rotor 130. As a result of that arrangement, the inner diameter of the bearing 121 is large. Accordingly, when the rotors 120 and 130 are rotated at a high speed, the bearing 121 becomes worn and, therefore, its useful life is shortened. Thus, the prior art rotor device is not entirely satisfactory.